Semiconductor spatial light modulators (SLMs) are suitable for digital imaging applications, including projectors, televisions, printers, and other technology. A DIGITAL MICROMIRROR DEVICE (DMD) is a type of SLM invented in 1987 at TEXAS INSTRUMENTS INCORPORATED of Dallas, Tex. The DMD is a monolithic semiconductor device based on micro-electromechanical systems (MEMS) technology. The DMD generally comprises an area array of bi-stable movable micromirrors forming picture elements (pixels) fabricated over an area array of corresponding addressing memory cells and associated addressing electrodes disposed under the micromirrors. The addressing electrodes are selectively energized by a control circuit with a voltage potential to create an electrostatic attraction force causing the respective micromirrors to tilt towards the respective address electrode. In some applications, the micromirror may be provided with a voltage potential as well. One embodiment of a DMD is disclosed in U.S. Pat. No. 7,011,015 assigned to the same assignee of the present disclosure, the teachings of which are incorporated herein by reference.
The monolithic nature of the design and build of the DMD pixel technology is associated with quasi-planar structures interacting electrostatically with the tilting micromirrors. This presents a problem with the ability to shrink structures while attempting to maintain electrostatic entitlement. In the end, the design becomes more and more sensitive to electrostatic torque delivery originating from the edges of planar members and all the variations that this can create.
The fabrication of the above-described DMD superstructure typically uses a CMOS-like process with a completed SRAM memory circuit. Through the use of multiple photomask layers, the superstructure is formed with alternating layers of aluminum for the address electrodes, hinges, spring tips, mirror layers, and hardened photoresist for sacrificial layers that form air gaps. The memory circuit may have a quasi-planar topography, and thus the quasi-planar topography may couple through the photoresist sacrificial layers and form quasi-planar structures.
Topography coupling of one layer to another layer during the monolithic fabrication of a semiconductor device, such as but not limited to layer topography coupling through a sacrificial photoresist spacer layer is expressed through how its shape is locked into place by a metal deposition which is sub sequentially shaped into a member. This member is defined as the ‘binge’ and the non-uniformity of it and other members, such as address electrodes and spring tips, has impact to the electrostatic torque delivery for actuation.